Hello all, can anyone help me with a BA luggage question? Thanks in advance.

Will be flying LIN-LHR-MEX next week in Club. I have a through ticket and I'm going out of my
way to fly TLS-LIN before hand partly because the fare goes down to 2600 euros instead
of 5000 from Toulouse but also because I am accompanying an elderly relative who lives in Milan.

I booked him a cash LIN-LHR ticket and then an Avios Club redemption from LHR-MEX on the same
flights as me.

Now am just wondering whether BA will accept to send his luggage straight through? I have categorically
been refused this at LIN and MXP before, even with a simple BA connection at T5. They have stated,
infuriatingly, that they can't do it on separate tickets.

I'd love to know the official answer on this if anyone knows it?

Or should I call the silver line as a third party nominee on his account and ask them to link
the two bookings, if that is sufficient?

Many thanks for your input.